Fishn…..
There are few that have the numbers of lines that I own. 1>9 wts. In floaters and <>10 sinking lines which don’t include various shooting heads.
The cost to try a bunch would be cost prohibitive for most. A starting point where the manufacturers provided the truth would certainly simplify the search for the line to match your casting style and equipment.
I weighed,with a RCBS powder scale, my 6 wt. lines the other day which are mostly Cortland and found them dead on to standard. A Sci. Ang. Ultimate Trout and a DT Mastery we’re also dead on. The results paralleled the information published in the manufacturers web sites.
Don